This invention relates to an engine speed control. More specifically, this invention relates to a method of using a control algorithm to improve the operation of a transmission.
Previous Control Algorithms for low power hydromechanical transmissions (HMTs) on small horsepower (<50 Hp) vehicles have proven to be lacking in responding to external loads and operator inputs in certain modes. These external loads include varying terrain, wheel slip conditions, and pulling loads. Operator inputs include throttle adjustments and braking changes. The goal for a control is for an operator to set a desired engine speed using the throttle and have the transmission control system adjust the transmission ratio to maintain that desired engine speed within limits as the external loading changes. When the vehicle speed is adjusted by the transmission ratio and does not match the desired vehicle speed for the operator, the operator must then make a manual adjustment of the Throttle.
Current transmissions using belt CVT's are open loop mechanical controls and are designed to handle these changes in operating conditions and operator inputs by responding to load as well as engine speed. Digital controls are either open loop or closed loop and typically respond only to engine speed. For optimum driving conditions a vehicle needs to reach near maximum engine torque quickly during accelerations and maintain this torque level at the engine crankshaft as the external loading and vehicle speed changes. A closed loop engine speed control alone does this adequately and so does an open loop engine speed with antistall algorithm as long as external loading does not vary rapidly. However, when extreme external load variations occur the current HMT systems cause the engine speed to vary beyond those of belt CVT's.
For an automotive controller, the throttle sets the maximum engine torque level for a given Throttle position and engine speed. At any throttle position, the transmission must adjust its ratio between drive shaft speed and engine speed to apply the commanded engine torque to the drive wheels including while accelerating or when experiencing variable external loading. The transmission ratio is adjusted in a way that attempts to keep engine speed nearly constant for a given constant throttle position. As the external torque loading increases, the transmission ratio must be reduced. As the external torque loading decreases then the ratio must be increased. Therefore, transmission ratio is increased if engine speed exceeds throttle set target speed and reduces ratio if engine speed is less than throttle set target speed.
Closed loop engine speed controls are sometimes used to operate the controller. During commanded engine speed-ups, torque loading is desired to increase at the drive shaft while continuously increasing the speed of the vehicle. During decelerations, the torque may decrease at the Engine output shaft and can actually change direction so that the engine absorbs torque from the transmission. Thus, the engine torque absorption is limited to a level typically less than 25% of accelerating torque for the same engine speed. Under conditions of deceleration with closed loop engine speed control, the transmission ratio is commanded to stay the same or increase without a throttle command. This results in engine speed staying high or over-speeding as the engine is unable to absorb all the torque at its output shaft. Therefore, the change in transmission ratio must continue to decrease to affect a timely stopping of the vehicle.
An open loop engine speed algorithm works to slow the vehicle down and prevent engine over-speeding because the algorithm does not tend to add transmission ratio when the throttle is released. However, when the throttle is reapplied while the vehicle is slowing down, the transmission ratio must decrease slightly from its current position or stay the same momentarily to allow the engine speed and torque to respond to the throttle command. This is necessary in order to increase transmission output torque and to accelerate the vehicle smoothly. Thus, present open loop control algorithm implementations require complicated logic to accomplish desired control with slow response resulting in delay of engine speed recovery during throttle reapplication.
Thus, it is a principal object of the present invention to provide an improved controller that provides for smooth driving conditions.
Yet another object of the present invention is to provide a controller that is able to process a plurality of input signals to accommodate an operator's input.
Another object of the present invention is to provide a method of operating a transmission that varies the ratio between the input and the output of a transmission without load influence.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.